1. Field of the Invention
This invention relates to memory modules for expanding memory capacity in computer systems and to memory module connectors.
2. Description of the Related Art
Both single in-line memory modules (SIMMs) and dual in-line memory modules (DIMMs) and corresponding memory module connector sockets for expanding memory with computer systems are well known Generally speaking, in-line memory modules include a printed circuit board on which a plurality of memory chips such as DRAMs are surface mounted. A connective portion along one edge of the printed circuit board is adapted for insertion into a mating (i.e. accommodating) space of a connector. A plurality of contact pads (also called pins) on the connective portion mates with a plurality of corresponding contacts inside the accommodating space of the connector to provide for the transfer of electrical signals between the memory module and the rest of the computer system.
On a SIMM, the connective portion usually includes a plurality of contact pads on either the front side of the edge of the printed circuit board or on both the front and back sides of the printed circuit board. In configurations that include contact pads on both the front and back sides of a SIMM, opposing contact pads on the two sides are typically shorted together and therefore carrying the same electrical signal. In a DIMM, the contacts are positioned in the connective portion on both the front and back sides of the printed circuit board. At least some of the opposing contact pads on the two sides of the printed circuit board of a DIMM are configured to carry differing electrical signals, thereby increasing the signal density without necessitating smaller contact pads or a larger printed circuit board.
FIGS. 1A and 1B illustrate two embodiments of prior art DIMM memory modules 100 and 150, respectively. Memory modules 100 and 150, as shown, include 84 contact pads, such as contact pads 115A and 165A, on the front side, for 168 total contact pads. It is noted that the number of contact pads may vary such that memory modules with up to 200 contact pads are available on the market.
Memory modules 100 and 150 are configured to couple to appropriate memory module connectors, which are specifically designed to mate and secure the memory module. In general, a connector comprises a housing including an accommodating space, which is adapted to receive a portion of the printed circuit board of the memory module.
Turning to FIG. 1A in detail, memory module 100 includes a printed circuit board 110. A region 103, shown with dashed lines, for the placement of semiconductor integrated circuits, such as DRAM memory chips or other appropriate memory, occupies the majority of the space on a face of the printed circuit board 110. The contact pads 115 are disposed along one edge (i.e. the connective portion) of the printed circuit board 110 from a short distance from the left end to approximately the same distance from the right end. The center of the length of the printed circuit board 110 is marked with a centerline 101. A single notch 120 is positioned along the one edge at substantially the center of the edge of the printed circuit board 110. In other known embodiments, notch 120 may alternatively be positioned approximately one-half of the width of the notch to either side of the center location, as noted with dashed lines. Additional details regarding the notches 120 may be found with respect to FIG. 1C below. The printed circuit board 110 also includes indentions 105A and 105B positioned on the left end and right end, respectively. The indentations 105A and 105B are shaped to receive module extractors, which may be included as a part of the connector, to hold the memory module 100 in place when the module extractors are in a closed position.
Turning to FIG. 1B in detail, memory module 150 includes a printed circuit board 160. The contact pads 115 are disposed along one edge of the printed circuit board 160. The center of the length of the printed circuit board 160 is marked with a centerline 151. A center notch 120A is positioned along the one edge at substantially the center of the edge of the printed circuit board 160. Memory module 150 also includes a left notch 120B positioned to the left of center. Similar to the center notch 120A, the location of the left notch 120B is also known in other embodiments to be repositioned approximately one-half of the width of the notch 120B to either side of the illustrated location. The printed circuit board 160 also includes indentions 105C and 105D positioned on the left end and right end, respectively.
FIG. 1C is a close-up view of a notch 120. As shown, notch 120 is located on the edge of the printed circuit board 110 or 160 in a space along the row of contact pads 115. The height of the notch 120 is just slightly higher than the corresponding size of the contact pads 115.
It is noted that the notches 120 are configured to mate with keys in the accommodating space in the housing of the corresponding connector. A center key, which is configured to mate with a center notch 120 or 120A, of the connector may be referred to as the xe2x80x9cvoltage keyxe2x80x9d, while the left key, which is configured to mate with left notch 120B, may be referred to as the xe2x80x9cfunctionality keyxe2x80x9d. The names refer to the different voltages and/or functionalities that the three locations for each key (and therefore notch) correspond, depending on the manufacturer or standard.
One problem associated with the memory modules 100 and 150 is the difficulty in correctly installing the memory module 100 or 150 in the corresponding connector. Even with installation guides as a part of the connector, the memory module 100 or 150 may be installed backwards or unevenly. While the use of a polarized two-notch memory module, such as memory module 150, may decrease the likelihood of installing the memory module backwards, the notches 120A and 120B may not aid in installing the memory module evenly. It may be possible to install the memory module 150 with a slight tilt leading to one or more misconnections or even shorts. A related problem is the stability of the memory module 100 or 150 once inserted in the corresponding connector. Additional stabilizing features may inhibit simple and accurate insertion, which may further lead to uneven insertion and improper connections. Thus, it can be seen that an improved memory module, connector, and system thereof with improved ease of insertion and stability are desired.
The problems outlined above are in large part solved by an improved memory module with offset notches for improved insertion and stability and an improved memory module connector configured to receive the memory module. In one embodiment, the connector includes a first end, a second end, and a center midway between the first end and the second end. The connector housing further includes an accommodating space for receiving a connective portion of a printed circuit board of a memory module. A first key and a second key are disposed within the accommodating space of the housing. The first key is positioned between the first end of the housing and the center. The second key is positioned between the second end of the housing and the center. A distance between the first key and the second key is greater than 40% of the length of the connector housing. In one embodiment, one or more of the first key and the second key extend from the accommodating space beyond a top plane defined by a top side of accommodating space of the housing. The distance between the keys may advantageously allow for greater stability for a memory module coupled to the connector without compromising ease of insertion.
In another embodiment, a memory module is contemplated that includes a printed circuit board including a connective portion configured to be inserted into a memory module connector. The connective portion of the printed circuit board includes a first end, a second end, and a center midway between the first end and the second end. A first notch and a second notch are positioned in the connective portion of the printed circuit board. The first notch is positioned between the first end of the printed circuit board and the center. The second notch is positioned between the second end of the printed circuit board and the center. The distance between the first notch and the second notch is greater than 40% of the length of the printed circuit board. In one embodiment, the first notch is farther from the first end of the printed circuit board than from the center, and the second notch is closer to the second end of the printed circuit board than to the center. The distance between the notches may advantageously allow for greater stability of the memory module while coupled to a connector socket without compromising ease of insertion.